A conventional reciprocating engine comprises an engine body in which the cylinders, normally four, are housed. Corresponding pistons reciprocate inside the cylinders and are linked to a common shaft, named crankshaft, by connecting rods, so that the reciprocating linear motion is converted to a circular motion.
By controlling the input and output of air or air enriched with fuel by means of some valves, the motion of the pistons produce in the cylinders variable volumes that correspond to the four known stages of a 4-stroke internal combustion engine: intake, compression, ignition/combustion/expansion and exhaust. Only during the expansion that takes place in each cylinder on half the revolutions, a torque is produced which drives the crankshaft with a force that is proportional to the consumed fuel, not counting the losses that arise when converting linear motion to circular motion. Theoretically, assuming that the pressure of the combustion gases is constant, the losses are of about 40%. Further losses due to the inertia of the masses in reciprocating motion, and to the friction of the piston against the cylinder wall when the pressure is high, ought to be added.
However, the pressure of the gases in the cylinder in the expansion phase is not constant but presents a high level at the beginning due to the higher temperature and the smaller volume, whereas at the end the pressure is lower because the volume is bigger and the temperature is lower. Besides, there is a residual pressure left that causes a noise in the exhaust pipe the intensity of which increases with the speed and load regime the engine undergoes. In fact, the higher the speed the less the temperature decrease, whereby the combustion is finished in the exhaust pipe. On the other side, the higher the load the more fuel with the right air proportion and the higher pressure at the beginning of the exhaust.
In order to mitigate these drawbacks, rotary internal combustion engines have been proposed, in which the ‘pistons’ move following a circular motion inside a toroidal ‘cylinder’, moving closer and moving away to allow for the compression and the expansion, respectively. The efficiency of these engines depends on the control of the variable speed of the ‘pistons’, since this speed determines the fulfillment of the stages of the engine, and hitherto no control mechanism that significantly improves the efficiency of a rotary engine with respect to the reciprocating engines, and that is further substantially free of mechanical problems, has been proposed; thus no rotary engine of this kind has ever been put to practice.